Small cause, large effect - Akvaryum Magazini 1

Any extarnal influence on reef communtiy can have dramatic effect on its ecology, but it may also buffered by the resilience of the ecosystem to deal with environmental impacts. The effect depends on the strength of the impact as well as the ability of the reef ecology to respond to it. Imagine a fringing reef stuated parallel to the coastline, as for example one year the beautiful Philippine Island of Guimaras. A river near the coast carries clean freshwater into the ocean. There is human activity on the land around the river, for example local farming and regular irregition. Suddenly, sediments from the river banks are washed down into the river. These sediments will obviously have substantial impact on reef ecology. The sea water will be clouded by suspanded solids and the corals will receive less sunlight since the photosynthetic activity of the algae will be inhibited. Corals that depend on the activity of the symbiotic algae will be threatened together with their symbiotic partners. This is the time for the filter feeders. They will be quite happy in cloudy conditions, as they can take advantage of an ecological niche now opening up to them. Before the impact, there would have been a fierce competition between them and the fast-growing corals with their symbiotic algae; any small sponge could be quickly overgrown by corals or algae. Now, free-floating algae and symbiotic algae of the corals will struggle againist the turbid water conditions leaving the filter feeders new room to live and feed.

The other reef inhabitants will be equally influenced by the impact. Herbivorous animals, like fish, snail, slugs, or sea urchins that used to feed on algae, either migrate out of the area or face starvation. The same holds true for all those animals that fed on herbivorous creatures, for example, those feeding on algae-eating snails. Others that live in symbiosis with specific corals, such s the small symbiotic crabs associated with Acropora colonies,or those that live within a Xenia sof coral, are likely to vanish from this particular area of the reef. Many other organism which, in some way another, belonged to the reef community that existed before the change, cannot adapt and so vanish. This opens new ecological niches and presents opportunities for those organisms that co-exist with filter feeders, such as brittlestars, various worms, small craps, filter-feeding mussels, and many other inhabtants able to cope with sediment-rich water. The change, in turn, brings new predators onto the scene, for example, certain starfish specialized in cracking mussels and feeding on their soft internal parts. If the changes lead to a further accumulation of organic waste, the bacterial community has to adapt and grow in order to cope with the new situation. All this makes clear how the whole reef community must continually reorganize if it is to cope with internal and external changes. Anyone keeping a reef tank tank should appreciate that an aquarium is an equally complex "organism", having numerous interdependencies between inhabitants. Smilar to the natural reef ecosystem, aquarium organisms in a reef community thrive to establish their own equilibrium. Any external influence will lead to a shifting community structure aimed at reinstating the previous equilibrium.

However, the system doesn't always succeed. A natural case-in-point is exemplified by a fringing reef from the Philppine province of Bolinao. The reef is situated parallel to the coasline at a dstance of about one kilometer. The area is heavily populated by local fishermen, who have fished this coastline as long as we can remember. Over time, the population has grown and people catch increasingly more fish, and produce more organic waste that is flushed into the ocean, particularly during the rainy season. The water in this area has become richer in nutrients, leading to increased algae growth. At the same time, the fishermen caught more fish, including the algae-eating species. Moreover, the fishermen have shown greater interest in the larger fish, that feed more people than the smaller ones. Within a short time, the most effective algae-eating fish were removed from the reef, and with them, the adult fish that could have produced more algae-consuming offspring. What was left were the small juvenile fish, hiding between the corals, and a blooming algae popultion.

3. Picture: A Philippine diver hunting for small fish. This area was once a fringing reef.
From The Successful Reef Aquarium Now, the hunt was on for the small fish. Bamboo sticks were used to lift the stony corals were broken into pieces and the small fish were chased out of their shelter. Consequently, the damaged coral colonies became overgrown by algae-eating organism. The result was a dying fringing reef covered in large areas by mats of algae.